Digital imaging devices, such as digital cameras, allow users to take photographs and store them in digital form. In general, digital imaging devices capture images by exposing an image sensor, such as a Charged Coupled Device (CCD), to a scene for a particular exposure time. As digital imaging technology advances, CCDs are able to capture images with greater resolution. The spatial resolution of a digital camera refers to the number of pixels included in a captured image. For example, a three-megapixel digital camera takes an image that is divided into three million pixels. As the pixel size decreases, it is increasingly important to ensure that each pixel is exposed to a sufficient amount of light to capture the image. For instance, the exposure time may be increased to ensure that each pixel captures enough light.
In general, typical digital imaging devices do not have enough sensitivity to capture images in many low light situations. For example, a user may wish to take photos in a museum or at a performance. In many of these cases, the user is not permitted to use a flash when taking the picture. Typically, the digital imaging device will set a very long exposure time (e.g., several seconds) to ensure that enough light is captured. However, the digital imaging device typically captures motion blurred images because the user cannot hold the imaging device steady enough during the course of the exposure. Furthermore, the subject of the photo may also move during the exposure, further blurring the captured image.
Some digital imaging devices also provide users with telephoto options to zoom in on a scene, enabling the capture of a closer version of the scene. As the zoom factor for capturing an image increases, the exposure time can be proportionally shortened. However, as the pixel sizes decreases in higher resolution imaging devices, the exposure time may not be proportionally shortened or shortened at all, to ensure that enough light is captured.
In general, there is a trade-off between shorter exposure images and longer exposure images. A short exposure image is typically sharp, as there is little motion blur. However, short exposure images are also typically noisy, as the signal-to-noise-ratio is low for underexposed pixels. Signal-to-noise-ratio decreases as the pixels in the image sensors receive less photons and short exposure images may not receive sufficient photons to ensure high signal-to-noise-ratio. In contrast, a long exposure image is well exposed and less noisy. However, as described above, long exposure images are subject to motion blur, resulting in blurred images.
In the prior art, motion stabilization of the image sensor is used to account for motion blur. Motion stabilization typically involves the image sensor being located on mechanical actuators that are controlled by a stabilizer circuit. If the imaging device moves, e.g., the photographer's hands shake, the actuators move the image sensor in the opposite direction, stabilizing the image sensor. Keeping the image sensor stabilized for the duration of the exposure reduces motion blur.
Motion stabilization using actuators is only effective for a small range of motion, due to the mechanical limits of typical actuators. Motion stabilization also places several limitations on imaging device. For instance, the mechanical actuators and stabilizer circuits are typically costly components. Moreover, they require substantial power to drive the actuators. The heat generated by the actuators also influences the image sensor, having an adverse effect on the quality of the captured images. Furthermore, due to the size of the actuators, there is a limit to the minimum size of the imaging device.